There are food processors of the type broadly set forth above having a working bowl or vessel with a motor-driven tool-drive mount in the bowl on which various selected rotary tools can be engaged to be driven for performing various food processing operations, such as listed above, as may be desired by the user. A detachable cover is secured over the top of the bowl during use. This cover includes a hopper or feed tube which has a mouth that opens downwardly through the cover into the top of the bowl. The food items to be prepared are placed in this feed tube and then are manually pushed down through the feed tube into the bowl by means of a removable pusher member which is adapted to slide down in the manner of a plunger into this feed tube. For further information about this type of food preparing apparatus, the reader may refer to U.S. Pat. Nos. 3,892,365 to Verdun and 3,985,304 to Sontheimer.
The rotary tools in food processors are being driven by relatively powerful motor drive arrangements and have the capability of causing injury. For this reason, a mechanical interlock bowl-cover safety switch is conventionally incorporated into these units. This switch arrangement requires that the cover be firmly locked onto the bowl in normal position before the motor will start. This requirement is achieved by making the cover, which locks rotationally to the bowl, with a projection or member which causes the closing of the switch carried in the housing only when the cover is properly locked into its normal position on the bowl. Depending upon the type of food processor, this cover projection may actuate the switch directly or through an intermediate linkage.
Another safety feature is the provision of an upright food-receiving hopper having a feed passageway which extends down through the cover. This hopper is deliberately designed in terms of shape, moderate cross-sectional area of the food feed passageway and height to make it almost impossible for a normal adult inadvertently to insert a hand sufficiently far down into the hopper to touch the rotating tool located in the upper portion of the working bowl. In addition, the pusher is provided for feeding food items down into engagement with the food processing tool.
Such mechanically actuated switches require that a mechanical access port be provided through which a plunger or other projecting member can actuate the switch. This access port is usually covered by a recessed, flexible displaceable diaphragm for preventing food materials or liquids from entering the base housing. The user is faced with the need to keep the access port and the recessed surface of the diaphragm clean for aesthetic and sanitary reasons. Moreover, such a flexible, displaceable diaphragm may be subject to aging or deterioration over long periods of time, making it more difficult to clean or to operate.
Accordingly, it is an object of the present invention to provide a safety interlock for the bowl and cover, and in some cases for the food pusher as well, employing magnetic effects to prevent operation of the motor drive unless the components are properly mounted and firmly held in place and thereby avoiding the need for any mechanical access port in the base housing. Consequently, the food processor is neater in appearance and easier to clean and to maintain.
In employing magnetic effects to provide the desired safety interlock feature, we recognize that simple magnet arrangements are undesirable because of the widespread use of small magnets in many home kitchens. Such readily available magnets might be used inadvertently or intentionally to defeat a safety interlock based upon a simple scheme. Accordingly, we have provided various embodiments of the invention employing magnetic effects and each including discriminating means for increasing their discrimination against inadvertent or improper actuation by ordinary magnets.